Method of forming and applying metal heat exchange fins



June 21, 1955 R. SMITH-JOHANNSEN 2,711,332

METHOD OF FORMING AND APPLYING METAL HEAT EXCHANGE FINS Filed Feb. 8 1951 Figl. 4

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United States Patent METHOD OF FORMING AND APPLYING METAL HEAT EXCHANGE FINS Robert Smith-Johannsen, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 8, 1951, Serial No. 209,923

1 Claim. (Cl. 154-117) My invention relates to heat exchange constructions, particularly those in the form of cooling fins for use on air or other fluid cooled apparatus. Another aspect of my invention relates to methods of forming such heat exchange fins from thin metal strips and of applying or securing the formed fins to structures as desired.

In the design of many kinds of electrical and mechanical equipment, it is desirable to provide metallic fins for dissipating heat to air or other fluid which passes the equipment. Where the equipment is of a fragile nature, or of small size, the effective attachment of the heat exchange fins presents quite a problem. The fins cannot be made of heavy gauge material if a desirable high ratio of heat exchange surface to bulk of the material used is to be maintained. On the other hand, if the fins are made of thin stock, it becomes clifi'icult to form the fins by prior known methods and to secure them in good heat exchange relationship to the body of the equipment where they are needed. My invention includes a design of thin metallic fins in continuous strip form, applied by a suitable adhesive to the body of equipment, and held in their formed shape and against the bod-y by the adhesive, as described below. Inherent in the design of the fins themselves, my invention also includes a method of forming the fins from a strip of thin metal by folding the metal, securing the folds of the fins to each other, applying the fin strip to an object, securing the fin strip to the surface of the object, and straightening or positioning the fins with respect to object after the fins have been secured in place.

Other objects and the details of one form of my invention and one method of producing it will be apparent from the following description and claim, taken with the accompanying drawing in which Fig. 1 is a greatly magnified sectional view through a portion of a sheet or tape used in practicing my invention; Figs. 2, 3, and 4 are enlarged diagrammatic edge views of tape sections showing progressive steps in the formation of a fin on a fin tape according to my invention; Fig. 5 is an enlarged fragmentary edge view of a fin tape in the process of being applied to the surface of a curved object; Fig. 6 is a similar edge view of a fin tape in the process of being secured to a flat surfaced object after being applied thereto; and Fig. 7 is an enlarged fragmentary edge view of a series of finished fins secured to a flat surface.

Metal, in the form of thin sheets or strips, is the principal material used in making heat exchange fins according to my invention. I have found aluminum and copper foils to be excellent for this purpose. Sheets up to ten mils in thickness are satisfactory for many applications, and are to be considered as included whenever the term foil is used in this application. Metal sheets above ten mils thickness, even beyond thicknesses generally regarded as foil, may be used according to my invention, if they can be shaped readily without damaging the material or the adhesive bond described herein. Foils as thin as three mils thickness have also provided useful. As will be clear later, each finished fin according to my invention 2,711,382 Patented June 21, 1955 will have a thickness at least double that of the starting sheet thickness.

In the manufacture of heat exchange fins (herein sometimes called cooling fins), it is desirable that a large surface of the fin material be exposed to the air, oil, or other fluid being used as the heat exchange medium. Furthermore, the cooling fins should be solidly attached to the surface of the object being cooled so that no air pockets exist which might slow down heat transfer. The fins themselves should also be free from air pockets for best results. For securing the folds of the fins to each other and also for securing the finished fin strip to the surface of an object, I have used various flexible silicone adhesive materials, such as those described in my copending patent applications Serial Nos. 77,043, 77,044, and 77,045, filed February 17, 1949, now Patent Nos. 2,602,408, 2,601,336 and 2,601,337 respectively, and Serial No. 190,241, filed October 14, 1950, now Patent No. 2,643,964, all assigned to the same assignee as the present application. By reference, these prior applications are made a part of the present disclosure. For the purposes of the present description, it is sufiicient to say that such adhesives may be applied evenly to the surface of metal, such as the foils or thin sheets used here, and tapes cut from such sheets, after covering the adhesive with a protective sheet of cellophane polyethylene, or similar material which does not readily adhere to the adhesive. A magnified section of such prepared tape is shown in Fig. l of the drawing, where 1 indicates the metal foil or sheet, 2 is the thin, even layer of flexible adhesive which is applied to the metal, and 3 is the cellophane protective backing sheet which may be peeled off from the adhesive when it is desired to stick the metal sheet to something.

The prepared tape of Fig. 1 may be readily stored and handled in the same manner as other pressure-sensitive or thermally-sensitive tapes. According to my invention, this starting tape is manufactured into a finished strip or tape of any desired width carrying a series of integral folded fins which may be of any desired height and be spaced at any regular or irregular intervals along the length of the finished strip. This finished tape with projecting fins I will call the fin tape.

In making the fin tape, the backing sheet 3 is first removed from the starting tape and the thin metal strip 1 is folded or crimped upon itself with the adhesive side innermost to form the desired fins at the desired spacing along the tape. The folded tape is then placed on a new backing 4, as shown in Figs. 2 through 5. The backing 4 may be of the same material as the original backing. Fig. 2 shows the end of the metal strip on the backing 4, with bends 5 and 6 made, which determine the height of the finished fin. A third bend 7, located the same distance from bend 6 as bend 6 is from bend 5, completes the fold forming a single fin 8. The folded fin is then pressed gently so that the facing adhesive surfaces are joined, and the fin is bent down flat on the surface of the finished fin tape, or on top of preceding fins on the tape, as shown more clearly in Figs. 5 and 6. Further fins are made in the tape at desired intervals, and the portions of the tape between the fins, as at 9, are covered by the backing 4.

The size and distribution of the fins may be controlled by a very simple crimping device which may be either hand or machine operated.

The resulting fin tape has an adhesive coated surface which may be readily applied against the surface of any object, with cooling fins located on the side opposite the adhesive. Because the fins lie more or less fiatwise on the tape, this fin tape with the protective backing in place is easy to store and handle without damage to the fins. Furthermore, the fin tape adapts itself readily to use in a the backing strip is removed (Fig. 5) and the tape is 1 positioned and lightly pressed against the surface of the object, S, to be provided with the fins. The adhesive exposed upon removal of the backing strip will hold the fin tape to the object to some extent by pressure alone.

However, for best results, and to obtain a firm, permanent bond between the fin tape and the object, the adhesive is preferably cured by the application of light pres sure and low heat when the tape is on the object. shows the application of a Weight W to a fin tape on a flat surface, the weight pressing the folds of the fins against each other and pressing the tape against the surface of the object S. The weight itself may be heated,

Fig. 6

as by using a sadiron, or the heat may be applied sepal rately. For one of the adhesives which I have used, a

light pressure for five or ten minutes at temperatures between 110 and 130 centigrade has been found suffi cient for proper curing of the adhesive in the folds of the fins and between the fin tape and the object. face of the object is round, as the circumference of a tube, the tape may be pressed on by wrapping it with several layers of stretched rubber. Heat for curing the adhesive may be applied in the field through the use of infra-red lamps. range may readily be obtained using such lamps.

After the fin tape is firmly secured to the object, as by the curing step described above, the fins may be straightened out by hand, or by the action of a suitable air jet,

If the sur- Temperatures within the desired curing or otherwise, and may occupy parallel positions vertical to the surface as shown in Fig. 7, or may be shaped or positioned in any desired form, depending upon the particular application. The adhesive, being flexible, will not break its bond in the folds of the fins and will maintain a solid joining of the fin strip to the object, free of objectionable air pockets or voids. With the silicone adhesives which I prefer to use, the life of the adhesive, as regards proper bonding and effective heat transfer, will be almost indefinite at operating temperatures up to 200 It will withstand the severe conditions of freezing,

C. thawing, and 100 per cent humidity without losing its effectiveness. Therefore, fins applied according to my invention should have an unusually long operating life in the absence of outside physical blows or similar mechanical damage to the fins themselves.

One rather unusual result in joining the fin folds and in securing the fin tape to the object by means of a flexible adhesive, is found in the lowering of vibration of the fins when the finned object is in use. This is attributed to a cushioning provided by the adhesive, which damps the vibrations. The nature of the silicone adhesive is such that it not only spreads evenly and thinly but it also retains its flexibility and adhesive qualities for long periods of time under extremes of operating temperatures.

It will be evident from the foregoing that certain aspects of my invention are not limited to the particular details of construction or the particular steps followed in the illustrated examples. Obviously, various and other modifications and applications of the invention will occur to those skilled in the art. It is, therefore, my intention that the appended claim shall cover such modifications and applications as do not depart from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

The process of applying metal cooling fins to an object comprising the steps of (1) applying a flexible heatcurable silicone adhesive to one entire face of a strip of thin metal foil, (2) forming a series of spaced folds in said strip with said adhesivecoated faces inside the folds, (3) securing the inner faces of said folds along essentially their entire length to each other by said adhesive to form a tape having spaced fins projecting from one face of the tape, (4) folding said fins flatwise against said tape and applying the adhesive-coated side of said tape to the surface of an object it is desired to cool, and (5) heating the total assembly to secure the adhesive-coated face of said tape to the surface of said object while maintaining said fins in the flatwise condition and to effect.

curing of the adhesive between adjacent faces of the fins thereby to obtain an object having cooling fins attached thereto which can be raised in a position perpendicular to the plane of the object and which can serve as heat-dissipating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,037,754 Gildersleeve Sept. 3, 1912 1,200,167 Carter Oct. 3, 1916 1,369,806 Haurner Mar. 1, 1921 1,679,973 Jacobs Aug. 7, 1928 1,721,808 Kettering July 23, 1929 1,924,472 Thomson Aug. 29, 1933 2,035,403 Przyborowski Mar. 24, 1936 2,133,357 Mazer Oct. 18, 1938 2,342,117 Brown Feb. 22, 1944 2,413,179 Grandmont et al Dec. 24, 1946 2,423,869 Blessing July 15, 1947 2,423,870 Blessing July 15, 1947 2,532,011 Dahlquist et al. Nov. 28, 1950 2,555,564 Berman June 5, 1951 FOREIGN PATENTS France July 2, 

